1. Field of the Invention
This invention relates to a keyboard apparatus for an electronic musical instrument which performs digital processing.
2. Description of the Prior Art
A method that has heretofore been employed to detect the depressed or released state of each of the keys on the keyboard is to sequentially scan the keys from a low-pitched to a high-pitch sound range or vice versa, thereby to detect the key depressed state in the form of a time-division multiplexed signal, as set forth, for example, in U.S. Pat. No. 3,610,799 entitled "Multiplexing System for Selection of Notes and Voices in an Electronic Musical Instrument." Registers are provided for extracting and storing signals representing the octave and the name of a sound of the depressed key from the time-division multiplexed signal. The number of such registers are generally limited by a maximum number of keys depressed to a dozen or so. Since writing in the registers is achieved with the abovesaid time-division multiplexed signal, even if the signals of the octave and sound name of the depressed key are already written in one of the registers, the time-division multiplexed signal is repeated and the signal corresponding to the abovesaid key is included therein. Then, it is necessary to effect a control so that the same content as that of the register having already written therein may not be written.
Further, when the key is released, only the key depressed signal is removed, so that it is necessary to extract the signals of the octave and sound name of the key for which the depressed signal has disappeared, to search for the register having written therein the same content as the abovesaid signals and to erase the content of the register or apply it as a fall start signal to an envelope control circuit corresponding to the register.